Novel Heat-Integrated Hybrid Distillation and Adsorption Process for Coproduction of Cellulosic Ethanol, Heat, and Electricity from Actual Lignocellulosic Fermentation Broth

Round 1

Reviewer 1 Report

The topic undertaken by the Authors is important and interesting from the point of view of current possibilities of cellulosic ethanol production, which requires both energy inputs and is cost-intensive. The Authors have proposed a cost-effective approach to its production, presenting different approaches in relation to the conventional method. In my opinion, due to a large number of abbreviations used by the Authors, it would be reasonable, for the better clarity of the paper, to prepare a list of them in a table, which would make it much easier to get acquainted with the content of the paper. While the introductory part, the methodology and the description of results are presented in an acceptable way, I think it is necessary to discuss the results, which is missing in this version of the article. Moreover, the content presented in the chapter "Conclusions" is mostly just a summary of what was previously described in the body of the paper.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and suggestions

1. I propose to transfer Table 1 to chapter 2 Material and Methods and supplement it with the item summing by Total and adding Elemental Analysis, information about the conditions can be placed under the table.
2. In Figure 1, the absorption process appears when the work concerns the adsorption process, or according to the authors, it is correct, because it concerns a different nature of the action.
3. Please, improve the descriptions of individual drawings, they are illegible. You should stick to the adopted rules - in accordance with the implementation of the process, and also with the indication of the most important elements. The description should refer to the system components presented in Figures.
4. I suggest accepting Figure captions in the same convention, for example Schematic of ...., or some other way. The components of a given process should be listed in the figure with their names.
5. For the sake of clarity of Figures 2 and 6, the chemical composition of the structural components can be transferred to separate tables.
6. There are inconsistencies between the data presented in the figures and the data presented in the text, e.g. in Fig. 6 turbine 1- 9.5 atm, 236 C- and 268 in tex. There are also smaller differences in this regard in the remaining figures. There must be full compliance of the presented data.
7. Table 4 is not complete, units are missing, full names should be provided. This table applies only to CE production process, but how it relates to Heat and Electricity.
8. The study lacks data presentation on economic and environmental of all structural alternatives compared to the conventional process. After all, it was one of the primary goals of the work.
9. No explanation of the abbreviations used.
10. There are errors: in the reference to Fig. 1 in chapter 3.2, there is no sufficient reference to the literature in terms of the methods used and the discussion of the obtained results with other researchers. use - the HDA abbreviation throughout the work
11. There is no statement or comparison at work of proposed heat-integrated HDA process for CE, Heat, Electricity coproduction with conventional process.
12. . I have objections to references, items are reported twice in the list (17, 18), please check the source carefully, complete the items and citation.
13. The conclusions presented are too general.

 

General comments

The work brings new elements. It requires thorough work to finally obtain a positive effect, meeting the criteria of credibility, reliable result and clear message. When resuming work:

- check the compliance of the data presented in the figures and tables with the text

- the work structure should be reorganized in the chapter 2 section

- complete the literature and cite the results of other researchers

- present data on economic and environmental analyzes

- Newly developed processes should be compared with conventional ones

- in addition, a great deal of care must be taken in compiling and presenting the results.

Author Response

Dear Reviewer,

Please see the attachment.

Best regards,

Author Response File: Author Response.docx

Reviewer 3 Report

Major Comments:

In this study, the authors have designed a cost-efficient method to produce cellulosic ethanol (CE). The CE plant was designed with a capacity of 120 kty of CE and optimized with ASPEN v10. Environmental and Cost assessments were also performed. The language used in this paper was technical and terms were explained clearly. However, some comments might be helpful. The world is shifting towards green energy resources and in this study, the focus is on developing a new fuel that’s raw materials that can be alternatively used as a food resource. The carbon footprint in the HI-HDA process can reduce 36.9% of carbon print from the conventional method. However, the carbon generated in this process is still a threat to global warming. The literature of this paper needs to be improved as very few citations were used and some of them repeated a lot. One citation is numbered twice. The process has a lot of environmental concerns and is restricted in different countries also it is sophisticated due to energy-intensive equipments. Overall, In the process of optimization, all factors were considered into calculations and readings and values are predictable and accurate. The diagrams are fully labelled and all inputs and outputs along energy consumption and equipment are fully labelled. Apart from the environmental concerns, this study can greatly improve the production of Cellulosic Ethanol that can reduce the load on other fossil fuels.

Specific Comments:

1. Page 2, Line 41: “the use of EG as the extracting solvent may cause several serious environmental issues”. This process is also restricted in several countries then why optimizing it?
2. Page 3, Line 22: “HDA was simulated and optimized based on NREL and Strømsnes processes”. Can you please explain where Strømsnes processes were used?
3. Page 4, Line 14: “lignin was also utilized for the production of heat and electricity.” How was it used for the production of electricity?
4. Page 5, Line 4: “Methane and combustible solids were then burned to produce steam”. This may increase the carbon footprint.
5. Page 5, Line 9: “In addition, UNIQUAC functional-group activity coefficients (UNIFAC) method was used to estimate the missing binary parameters”. How was NREL used along UNIQUAC with the UNIFAC method?
6. Page 5, Line 14: “the total number of trays and feed location was adjusted to minimize”. Why minimize the number of trays if you can get less energy consumption at some higher no of trays?
7. Page 5, Line 22: “A Chemical Engineering Index of 596.2 (corresponding to 2020) was used to update the TIC estimates”. Chemical Engineering Index is reliable for equipment cost calculations not including operating cost.
8. Page 6, Line 3: “Gadalla’s modular method was applied to calculate the CO2 emissions”. How Gradalla’s model can accurately predict CO2 emissions?
9. Page 7, Line 5: “First, the fermentation broth was pressurized from 1 atm to 6 atm before being preheated”. Why was pressure increased as the heating was enough for the process?
10. Page 8, Line 4: “split factor of 1.0 and 0.05, for solid”. Any reason for choosing these split factors?
11. Page 8, Line 10: “calculation is based on the combined chemical oxygen demand (COD)”. Please specify the formula also.
12. More recent research about types of lignocellulosic biomasses, environmental pollution and renewable energy development should be added to make the background and discussion more strong: Fuel, 2021;293:120485. Renewable Energy, 2020;160:1253-64. Journal of Environmental Management, 2021;287:112257. Industrial & Engineering Chemistry Research, 2016;55(27):7411-30. Journal of CO2 Utilization, 2020; 40:101193.
13. Page 8, Line 15: “oxygen with 100% conversion”. Which software was used for simulation and what were the parameters?
14. Page 11, Line 32: “The C2 pressure was kept constant”. If C1 pressure is lowered, then why c2 was kept constant?
15. Page 12, Line 11: “HI–HDA process can save up to 80.4% and 43.5% of energy requirements in the condensers and reboilers.” In comparison to conventional process or HI process?
16. Please mention the pump head in Figure 2.
17. Reference Number 17 and 18 are the same.
18. References: The authors are advised to revise this section, including the latest reference. Please see some suggestions in the specific comments and in the ‘introduction’ section.

Author Response

Dear Reviewer,

Please see the attachment.

Best regards,

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper has been improved, and in my opinion it can be published  in its present form, however the discussion was developed in a limited extent.   

Author Response

We would like to express our deepest gratitude to the reviewer for the invaluable comments to improve the manuscript. We have carefully read and edited the manuscript to make it ready for publication.

Reviewer 2 Report

My comments were taken into account by the authors. Please exercise due diligence in the final preparation of the article.

Author Response

We would like to express our deepest gratitude to the reviewers for their invaluable comments to improve the manuscript.

Reviewer 3 Report

The authors have addressed most of the comments; they have also tried to make changes according to the reviewers’ suggestions. After revisions, the quality of the manuscript has been adequately enhanced. Therefore, the manuscript could be considered for the publication in the Journal. However, there are still some editing/ syntax errors present in the manuscript which need to be corrected, hence the publishing team is advised to read the manuscript carefully before publishing.

Author Response

We would like to express our deepest gratitude to the reviewers for their invaluable comments to improve the manuscript.

Besides, we have carefully re-read the manuscript to correct the syntax errors in the revised manuscript.